Add spanish as an example

Adding a new language without nlp requires now only to fill out the
pieces:

- define a list of month names to support date recognition
- add it to joex' dockerfile to be available for tesseract
- update the solr migration/field definitions
- update the elm file so it shows up on the client

modules/common/src/main/scala/docspell/common/Language.scala

@@ -47,7 +47,12 @@ object Language {
     val iso3 = "ita"
   }
 
-  val all: List[Language] = List(German, English, French, Italian)
+  case object Spanish extends Language {
+    val iso2 = "es"
+    val iso3 = "spa"
+  }
+
+  val all: List[Language] = List(German, English, French, Italian, Spanish)
 
   def fromString(str: String): Either[String, Language] = {
     val lang = str.toLowerCase